The present invention relates to a method and apparatus for automatically producing bags wrapped in cartons. Such a bag is a compound container combining inside an outer carton a bag made of plastic film, moisture-proof paper, or stuck-together sheet made of paper or plastic film and a metal foil.
In general, a bag wrapped in carton has often been used in the past as a compound container to be filled up with or to have sealed inside it various solid, powder or liquid products that need airtight packing or moisture-proof packing, for example snack foods such as biscuits and potato chips, detergent and medicine items, etc.
One of the most common methods for making such a bag involves a system that produces a carton with a bag inside it. This system is one in which an intermittently rotating multi-step mandrel is used.
This known method comprises wrapping a sheet of bag material around an intermittently rotating forming block by using an apparatus comprising forming blocks attached to the tip of a multi-step mandrel which can rotate horizontally, sealing the side seam and the bottom portion to form a bag, and bonding the carton material to the bag while wrapping the carton material over it to form an outer carton. In this method, wrapping of the bag material, sealing movements, and wrapping of the carton material have to be conducted when the intermittently rotating mandrel is stopped. Therefore, it has been found that it is difficult to increase the speed at which a bag-in-carton is produced. Also, the intermittent mechanism of the mandrel is prone to breakdown or failure because each portion of the mandrel repeatedly stops and starts moving. Moreover, the carton material and the bag material have to be supplied with mechanically accurate synchronization, which requires the intermittent mechanism to be complex and highly precise. Further, in this method, the bag material may cause such troubles as curling itself up because of static electricity, or difficulty in fitting to the forming block, unless the bag material has appropriate stiffness. Because of these problems, completed products have tended to have a drawback, that is the increased cost of production. Another defect in this known method is that, when the size of the carton material or the bag material is to be changed, it is quite labor-consuming and time-consuming to change and adjust a number of forming blocks attached to the mandrel. Therefore, it has been found that changing the size has been practically extremely difficult.
In another typical method for producing bags of the type under consideration, a bag and a carton housing have been made separately. The bag has been stuffed with the product to be packed, and then this bag has been inserted into the carton. In this method, since the bag is pre-loaded with the product, the bag tends not to be evenly shaped and its middle portion tends to get bigger. Therefore, the contact between the bag and the carton makes it difficult for the bag to be tightly inserted into the carton. This leads to the introduction of a process in which the loaded bag is stroked from both ends to reform the bag. However, the product in the bag can be damaged during this process, and the bag material is required to have appropriate stiffness because the bag is stroked by machine or hand. Also, in order to prevent said trouble and to increase the efficiency of assembling the bag and the carton, it is not possible to use a flat, thin carton. Further, the cross-sectional size of the carton has to be made quite large compared with that of the bag, and the cross-section of the carton has to be similar to a square, which is deficient. Therefore this method of production fails to be suitable for various needs of the market because the aforesaid deficiencies cause the cost to increase and restrict the shape of the carton.
In addition, carton packages used for transporting, storing or selling goods are generally required to have a large printing space available on the front portion thereof for advertising and promoting the goods stored inside the packages. Because of this, most of the carton bags are of a rectangular cross-section and a few of them are square. And, in order to increase the front space on the carton bag packages, its width is often changed but not the depth. Since making of the carton packages is carried out while the carton blanks advance in a column with longer sides of the carton blanks parallel to the direction of the production line of the apparatus for producing such a carton bag, it is impossible to make each carton advancing pitch smaller than the longer side of the carton blank.
Also, in regard to the method of producing a so-called bag-in-carton, U.S. Pat. No. 4,089,255 discloses a method by which a flat bag is put in an open-mouthed carton; vacuum pads reach both sides of the bag and automatically open the mouth of the bag when the carton comes to the stopping position; then air is blown into the bag from an air duct thus preparing the bag to be filled with a product. The problem with this method is that the conveyor has to operate intermittently and that such steps as supplying the bag, opening the mouth of the bag, and blowing air into the bag should be carried out while the conveyor is stopped during the intermittent process. Also, it has been found that the bottom portion of the bag is not fully inflated even when air is blown into the bag, which should be improved.